The "consensus" is that time started at the Big Bang and there is no meaningful referent for "before the Big Bang". However, the consensus is also that the theory that says this is flawed in several known ways, not least of which is the lack of unification between quantum and relativistic gravity that you may have heard about. This is the consensus theory not because it is perfect, but because nobody has yet managed to put together an alternative that does better across the board. Really the upshot is that nobody really knows, even for small values of "know".